Impaired physical fitness and insulin secretion in normoglycaemic subjects with familial aggregation of type 2 diabetes mellitus.

: Randomized subgroups from a health screening population were reinvestigated with oral glucose tolerance tests (OGTT) with simultaneous insulin and C-peptide measurements and submaximal exercise tests. Twenty-two normoglycaemic non-obese males with a strong family history of Type 2 diabetes were compared to 51 controls. While glucose levels tended to be somewhat higher, there was a tendency towards lower insulin and C-peptide levels in the hereditary group compared to controls, especially during the early phase of the OGTT, as reflected in a significant difference in the 40 min insulin level and the 0-40 min increment. Estimated maximal oxygen uptake was significantly lower in the hereditary group as were the sum ratios of insulin and C-peptide to glucose in the early phase of the OGTT. Insulin to C-peptide ratios did not differ. The data support both a decreased physical fitness, indicating peripheral insulin insensitivity, and a decreased insulin secretion among normoglycaemic individuals with familial aggregation of Type 2 diabetes.